Copper alloys have been proven as materials for bearings for decades. On account of their microstructure and properties, they satisfy the demands imposed on them particularly well. Wrought materials are often used during production and, on account of hot-forming and cold-forming, form a uniform and fine-grained microstructure that is particularly advantageous under sliding stress. The required strength properties can be set by means of microstructural transformation within certain ranges, with the result that the ability to withstand loads and the resistance to wear can be increased.
However, particular demands are imposed on the running surfaces of the sliding partners which are in contact with one another. By using lubricants, a supporting lubricating film is built up by virtue of the adhesion and viscosity of the lubricants, the intention of which is primarily to reduce wear. The surface condition of the running surfaces, in the context of the formation of a lubricating film over the area, has a crucial influence on the service life of a bearing. However, the occurrence of dirt particles has a particularly adverse effect on the service life, whether through abrasion of the bearing surfaces themselves or through introduction between the running surfaces via lubricants.
It is known to produce a targeted surface structuring of the running surface by means of special precision-machining processes. Examples include honing processes, as are used for cylinder liners in internal combustion engines. Machining processes of this type introduce a very fine lubricating pocket system into the liner, with the result that the oil cushion which forms over a lubricant deposit improves the sliding properties and reduces the wear. Furthermore, it is also known to use a laser to structure the surface. In this case, although the shape and position of the individual lubricating pockets can be set in a targeted way, this process is hugely time-consuming and correspondingly expensive as small-scale production.
Moreover, document DE 101 57 316 A1 has disclosed a bearing with a nanoscopically rough bearing surface, and a process for producing a bearing of this type. A bearing surface of this type is intended to improve the bearing properties, in the form of minimizing the formation of particles and reducing the friction. The nanoscopically rough bearing surface is produced by etching, mechanical roughening or by an electrochemical process. In the case of etching, the surface is treated with an optionally heated acid, for example by chromosulfuric acid or sulfuric acid. Suitable materials mentioned for the formation of a nanoscopically rough surface are metal alloys based on iron, titanium or chromium.
Furthermore, document DE 100 47 775 C1 has disclosed copper/aluminum multicomponent bronzes for use as bearing material in engine construction. In the use described, the running surfaces remain untreated, the assumption being that with these high-performance bearing materials tribo-oxidation layers will form after a short running time. These are thin layers which form as a covering layer by means of a chemical reaction as a result of heat and a high contact pressure. In general, these thin layers are desirable, since they reduce the coefficient of friction of the running partners and protect the base material from wear.